Method and apparatus for making welded large pipes

Abstract

In a method and apparatus for making welded large pipes, a leading end of a hot strip is connected to a trailing end of a leader strip and then subjected to a two-stage leveling for strip flatness in transverse direction and strip flatness in longitudinal direction. The entire surface of the hot strip including strip edges thereof is inspected by ultrasound and the strip edges are prepared in four stages before being pre-bent. The hot strip is then shaped into a slotted tube and the strip edges are welded along the inner and outer sides by laser to produce the pipe. Online process diagnostic is provided for monitoring the welding step and the finished welded pipe diameter is measured through online measurement. Online determination of a profile of a welded seam configuration and computer tomographic determination and evaluation of flaws inside the pipe, as well as ultrasonic inspection of the welded seam are further provided.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application claims the priority of German Patent Application, Serial No. 103 31 000.2, filed Jul. 3, 2003, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] The present invention relates to a method and apparatus for making welded large pipes, in particular helical-seam pipes, from hot strip of steel. [0003] Welded large pipes involved here include longitudinally welded pipes or helical-seam pipes, whereby helical-seam pipes are made at a diameter range of about 400 mm to 3050 mm and at wall thicknesses of 5 mm to 30 mm, and involve pipes which are continuously shaped into helical pipes with constant radius of curvature from a hot strip or sheet metal in a shaping device, whereby converging edges of the strip are welded together. Unlike a manufacture of longitudinally welded pipes which require a particular sheet metal width for each pipe diameter, hel...

AI Technical Summary

Benefits of technology

[0039] After leveling and edge preparation, quality assurance of the end product is carried out by inspecting the hot strip through ultrasonic technique for flaws, without destruction, across the entire length and width. Subsequently, the hot strip with the prepared strip edges are brought together in helical shape through application of conventional guiding and control systems in such a manner that the edges converge gap free and few degrees before the 6 o'clock position. In this position, the slotted tube is welded on the inside through laser welding. Suitably, the edges are slight bent so that the edges can be brought together without offset and free of gaps. The offset-free convergence of the edges can be assisted by a particular rolling tool in the welding spot of the 6 o'clock positi...

Problems solved by technology

Oftentimes, these regions are characterized by a shortness of water and underdeveloped infrastructure.

As a result, transport of pipes and logistics becomes time-consuming and costly.

In addition, the economy of countries in such regions is frequently precarious and foreign currencies are scarce so that attempts are underway to avoid import of goods and to increase own efforts to satisfy the demand.

This process is thus time-consuming and unsuitable to satisfy demands for current welding techniques and continuous process control.

As this process is intended for a long-term stationary operation, its application is also unsuitable for single-purpose plants which require a quick set up and which can be quickly put into operation.

In summary, the process described in the Stahlrohr Handbuch has the following shortcomings: very long manufacturing chain with many inspection and control steps, resulting in a very outsized and cost-intensive structure; transfer of the plant from site to site (mobility) is cost-intensive and time-consuming; submerged-arc welding results in a...

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